1. Field of the Invention
The present application relates to perpendicular recording heads for use with magnetic storage media. More specifically, the invention relates to the use of high saturation magnetic moment and low saturation magnetic moment layers within the main pole to produce high recording densities and low manufacturing costs.
2. Description of the Related Art
Recording heads for use with magnetic storage media have typically been of the longitudinal type, utilizing a pair of opposing write poles with their tips in close proximity to each other at the bottom surface of the recording head. The two poles are connected typically at the top by a yoke, typically made of the same ferromagnetic material as the poles. A coil is located in close proximity to one of the two opposing poles. When current passes through the coil, magnetic flux is induced in the yoke which produces a magnetic field with a bubble-like contour, across a gap separating the two poles. A portion of the magnetic flux across the write gap will pass through the magnetic storage medium, thereby causing a change in the magnetic state within the magnetic storage medium where the head field is higher than the media coercive force. The media coercive force is chosen high enough so that only the head fields across a narrow gap of a thin film inductive head, flowing with a slider on a air bearing between the surfaces of the disk and the slider, modify the bits of information on the storage media.
The bits of information are recorded on the disk along concentric tracks that are separated by guard bands. The width of the track plus that of the guard-band in which no information is stored defines the track density. The length of the bit along the track defines the linear density. The total storage capacity is directly proportional to the product of track density and linear density. The increase in linear density also enhances the data transfer rate. The demand for higher storage capacity and higher data rates led to the redesign of various components of disk drives.
The recording densities possible with longitudinal recording are limited to approximately 50 to 100 G bit/inch2, because at higher recording densities, superparamagnetic effects result in magnetic instabilities within the magnetic storage medium.
Perpendicular recording has been proposed to overcome the recording density limitations of longitudinal recording. Perpendicular recording heads for use with magnetic storage media typically include a pair of magnetically coupled poles, consisting of a main write pole having a small bottom surface area, and a flux return pole having a large bottom surface area. A coil is located adjacent to the main write pole, for inducing a magnetic field between that pole and a soft underlayer. The soft underlayer is located below the recording layer of the magnetic storage medium and enhances the amplitude of the field produced by the main pole. This in turn allows the use of media with higher coercive force, consequently, more stable bits can be stored in the media. In the recording process, an electrical current in the coil energizes the main pole, which produces a magnetic field. The image of this field is produced in the soft underlayer, such that about double the field strength is produced in the magnetic media. The flux density that diverges from the tip into the soft underlayer returns to the main pole through the return flux pole. The return pole is located sufficiently far apart from the main pole, such that the soft material of the return pole does not affect the magnetic flux of the main pole, which is directed vertically into the hard layer and soft underlayer. Strong magnetic recording fields permit the use of high anisotropy magnetic recording media. Therefore, significantly higher recording densities may therefore be used before magnetic instabilities become an issue.
Presently available perpendicular recording systems use main write poles having uniform magnetic properties (although some presently available longitudinal write poles include material having a high saturation magnetic moment on the surfaces facing each other). Such write poles are therefore limited by the difficulty in depositing material having a high magnetic moment to form the main write pole. Additionally, presently available write poles lack the ability to generate very localized magnetic recording fields, which are important for minimizing the trackwidth necessary to accommodate the skew angle.
Accordingly, there is a need for a perpendicular recording head having a main write pole made from material having a high magnetic moment, that is also easy to manufacture. Additionally, there is a need for a perpendicular recording head having a main write pole generating a highly localized magnetic recording field.
The preferred embodiments of the present invention are a perpendicular recording head having a main pole with a layer of high saturation magnetic moment material and a layer of low saturation magnetic moment material. The low moment material is tapered towards the pole tip, so that magnetic flux is focused into the high moment material before writing to the magnetic storage medium.
A typical perpendicular recording head includes a main pole, a flux return pole magnetically coupled to the main pole through a yoke, and an electrically conductive coil adjacent to the main pole. The bottom of the flux return pole will typically have a surface area greatly exceeding the surface area of the main pole""s tip. Electric current flowing through the coil creates a magnetic flux through the main pole. The direction of the flux may be reversed by reversing the direction of current through the coil.
A typical magnetic storage medium includes a recording layer having a plurality of magnetically permeable tracks separated by guard bands. A magnetically permeable lower layer, which is magnetically soft relative to the tracks, is located below the recording layer.
The main pole includes a layer of material having a high magnetic moment, and a layer of material having a low magnetic moment. The high moment material may be located adjacent to the yoke, with the low moment material located at the rearmost portion of the main pole. The low moment material is tapered towards the pole tip, so that the pole tip itself includes only high moment material. Manufacturing such a recording head begins by providing a substrate upon which a conventional read element and associated shields, flux return pole, yoke, and coil have been deposited. Photoresist is applied to the surface of the back of the recording head defining the location of the main pole""s high moment material. It is very difficult to plate or deposit high thicknesses of high moment material. Therefore, only a thin layer of photoresist is necessary to define the location of the high moment material, corresponding to the low thickness of the high moment material. Therefore, the photoresist may be applied defining a location for the main pole having a very narrow width, while maintaining a low aspect ratio (depth divided by width) in the channel defined by the photoresist, thereby facilitating accurate deposition of the photoresist. The high moment material is then deposited in the channel defined by the photoresist. After performing ion milling to remove any excess high moment material, a bi-layer photoresist is applied to define the shape and location of the low moment material. The use of a bi-layer photoresist permits a xe2x80x9cshelfxe2x80x9d to be formed within the upper layer of photoresist, thereby defining the taper of the low moment material towards the pole tip as the low moment material is being deposited. Depositing the low moment material and removing the photoresist completes the recording head.
To use the recording head, the recording head (or slider) is separated from the magnetic storage medium by a distance known as the flying height. The magnetic storage medium is moved past the recording head so that the recording head follows the tracks of the magnetic storage medium. Current is passed through the coil to create magnetic flux within the main pole. The combination of low moment and high moment material within the main pole provides a sufficiently thick channel for the magnetic flux to generate a strong magnetic field. The taper of the low moment material near the pole tip will focus this magnetic flux into the high moment material, thereby generating a strong magnetic field within the narrow area defined by the high moment pole tip. This magnetic field will cause the magnetic domains in the tracks to align with the magnetic field of the main pole. Changing the direction of current changes the direction of flux created by the recording head, and therefore changes the magnetic fields within the magnetic storage medium. A binary xe2x80x9c0xe2x80x9d is recorded by maintaining a constant direction of magnetic flux through the main pole, and a binary xe2x80x9c1xe2x80x9d is recorded by changing the direction of magnetic flux through the main pole.
The strong magnetic fields provided by this main pole structure permit the use of a magnetic storage media having a high anisotropy, thereby limiting superparamagnetic instabilities at high recording densities. Additionally, a narrow main pole may be defined during manufacture due to the low thickness of material deposited and resulting low aspect ratio of the channel within the photoresist wherein the main pole will be deposited. Lastly, the highly localized magnetic field defined by the small bottom surface area of the high moment material at the pole tip, permits the use of a narrower trackwidth while avoiding problems created by the skew angle, because the trackwidth is required only to accommodate the small bottom surface area of the high moment layer of the write pole.
It is therefore an aspect of the present invention to provide a perpendicular recording head having a main pole with one layer having a high saturation magnetic moment, and a second layer having a low saturation magnetic moment.
It is another aspect of the present invention to provide a perpendicular recording head wherein magnetic flux within the main pole is focused towards a layer having a high saturation magnetic moment at the pole tip.
It is a further aspect of the present invention to provide a perpendicular recording head having a main pole with a narrow width, corresponding to a narrow trackwidth.
It is another aspect of the present invention to provide a main pole for a perpendicular recording head having a sufficiently wide path for a strong magnetic field throughout its body, while focusing this magnetic field onto a narrow bottom surface area at the pole tip.
It is a further aspect of the present invention to minimize the effects of the skew angle upon the necessary trackwidth.
It is another aspect of the present invention to provide a main pole for a perpendicular recording head that is easy and cost-effective to manufacture.